- A team of University of Chicago scientists discovered a link at the atomic level between photosynthesis and exciton condensation.
- The condensate allows energy to flow without friction through the material.
- Researchers suggest the findings may one day offer new ways to design electronics.
PRESS RELEASE — Inside the laboratory, scientists marvel at the strange state that forms when they cool atoms to near absolute zero. Outside his window, trees collect sunlight and turn it into new leaves. The two seem unrelated—but a new study from the University of Chicago shows that these processes are not as different as they might appear on the surface.
Studies published in PRX Energy on April 28, a link was discovered at the atomic level between photosynthesis and exciton condensation—a strange physical state in which energy allows energy to flow without friction through a material. The findings are scientifically interesting and may suggest new ways to think about designing electronics, the authors say.
“As far as we know, these areas have never been connected before, so we find this very exciting and interesting,” said study co-author Prof. David Mazziotti.
Mazziotti’s laboratory specializes in modeling the complex interactions between atoms and molecules because they exhibit interesting properties. There’s no way to see these interactions with the naked eye, so computer modeling can provide scientists with a window Why those behaviors occur—and can also provide a foundation for designing future technologies.
Specifically, Mazziotti and study co-authors Anna Schouten and LeeAnn Sager-Smith have modeled what happens at the molecular level when photosynthesis occurs.
When a photon from the sun hits a leaf, it triggers a change in specially designed molecules. The energy knocks electrons loose. The electrons, and the “holes” where they were, can now move around the leaf, carrying the sun’s energy to other areas where it triggers chemical reactions to make sugar for the plant.
Together, the traveling electron-and-hole pairs are referred to as an “exciton”. When the team took a bird’s eye view and modeled how many stimuli moved, they noticed something odd. They see patterns in the pathways of stimuli that look very familiar.
In fact, this is very similar to the behavior of matter known as the Bose-Einstein condensate, sometimes known as the ‘fifth state of matter’. In this material, stimuli can be connected to the same quantum state — like a set of bells all ringing in harmony. This allows energy to move around the material with zero friction. (This kind of strange behavior intrigues scientists because they can seed extraordinary technologies — for example, a similar state called superconductivity is the basis for MRI machines).
According to the model devised by Schouten, Sager-Smith and Mazziotti, leaf stimuli can sometimes be connected in a similar way to the condensation behavior of stimuli.
This is a big surprise. Exciton condensate has only seen when the material is cooled significantly below room temperature. It’s like watching ice cubes form in a cup of hot coffee.
“Photosynthetic light harvesting takes place in a system that is at room temperature and what’s more, the structure is disordered—a very different way from the cold, pure crystalline materials you use to make exciton condensation,” explains Schouten.
The effect isn’t total — it’s more akin to “islands” of condensate formation, scientists say. “But it’s still enough to improve energy transfer in the system,” said Sager-Smith. In fact, their model suggests the efficiency could be doubled.
This opens up several new possibilities for producing synthetic materials for future technologies, said Mazziotti. “The ideal exciton condensate is sensitive and requires many special conditions, but for realistic applications it is interesting to see something that increases efficiency but can occur under ambient conditions.”
Mazziotti said the findings also play into a broader approach his team has been exploring for a decade.
The interactions between atoms and molecules in processes like photosynthesis are so complex—even supercomputers difficult to handle—that scientists have traditionally had to simplify their models to handle them. But Mazziotti thinks some parts need to be left out: “We think local electron correlations are very important for capturing how nature actually works.”
The study was partially supported by the National Science Foundation’s QuBBE Quantum Leap Challenge Institute.
Quote: “Exciton-Condensate-Like Energy Transport Amplification in Light Harvesting.Schouten, Sager-Smith, and Mazziotti, PRX Energy, April 28, 2023. .
Funding: US National Science Foundation, US Department of Energy.